1. Field of the Invention
The present invention relates to sensors, and more particularly, to a vertical type sensor.
2. Description of Related Art
In the field of medical therapy, it is a trend to develop a sensor, such as a sensor for detecting biological molecules. Particularly, in order to achieve instant measurement and monitor chronic diseases, it is the major trend to develop a detecting method which has high sensitivity, instant and precise detection, and reproducibility.
U.S. Patent Application Publication No. 20020092342 discloses a gas sensor, as shown in FIG. 10, including a back electrode 71, a SiC semiconductor layer 72 formed on the back electrode 71, an aluminum nitride layer 73 formed on the SiC semiconductor layer 72, and a gate electrode 74 formed on the aluminum nitride layer 73. The gate electrode 74 is a porous catalytically active metal electrode for forming an ionized product after the reaction of the target gas and the gate electrode 74, and then the ionized product diffuses to an interface of the aluminum nitride layer 73 and the gate electrode 74, so as to change potential distribution and voltage shift, thereby achieving the detection. Similarly, U.S. Patent Application Publication No. 20020020853 and U.S. Patent Application Publication No. 20090113992 disclose the usage of catalytically active metals.
In addition, H. T. Wang et al., APPLIED PHYSICS LETTERS 86, 243503 (2005) and F. Razi et al., Sensors and Actuators B: Chemical 146 (2010) 53-60 disclose a horizontal type sensors. In H. T. Wang et al., the zinc oxide pillar is formed by vapor deposition, and then the position of the electrode is defined. The gas concentration is identified by the horizontal type sensor based on the change of resistance; however, the stability of such horizontal type sensor is not so satisfied due to the significant variation of pillar distribution. In the horizontal type sensor of F. Razi et al., the substrate is made of porous p-typed silicon, and palladium is deposited on the silicon substrate, wherein hydrogen is trapped by palladium, and the porous silicon substrate is used for carrying palladium rather than detecting the target gas. Further, the metal electrodes, made of different materials, of the horizontal type sensor are identified by photolithography, such that the fabrication is complicated.
Therefore, there is a need to develop a sensor with high sensitivity, instant measurement, easy-to-read signal and reproducibility.